Well, not that many really famous people, most of them are in motorsport... I stress I am not an autograph hunter, that's chavvy and shallow in my opinion, anyway...
Jenson Button, he was at Silverstone for the BTCC a few years back (spectating obviously), my car had broken down in the paddock car park, he was stationary in his old CLK DTM, so we tapped on the window and asked if he had any jump leads...

he didn't... my friend asked him why he split up with Louise... um, whatever her name was.. as she was 'well fit'?, ... he put the window up

.
On the same day I met UK TV presenter
Mike Brewer, REALLY nice bloke, also asked him for jump leads, he had none either
Kimi Raikkonen was getting into his Merc when I went in for a hand shake, said hello and stuff, he still had my hand when one of his minders shut the car door - THAT was CLOSE!
Robert Kubica... back in the days when he was only 3rd driver for BMW Sauber, I asked him when he would get Villeneuves drive, at the time he laughed.. within a couple of months - it happened. I also met
Lucas Digrassi and
Faurus Fauzy that day, but that was when they were Formula Renault drivers, therefore more than happy to chat to anybody...
Literally bumped into
Rubens Barricello in the paddock at Silverstone.. he's quite short, and sweaty!
Nearly met Fernando Alonso, but he blanked me and his minder shoulder barged me out of the way.
Murray Walker.. is a miserable git, and would only talk to us if we bought a copy of his book, all we wanted to do was get him to say hello to my 4 & 5 year old god children... also met MotorsTV commentator
Martin Haven (nice bloke), ex F1 pundit
Tony Jardine (nice bloke), ex racer and TV presenter
Tiff Needell... errrm, also BTCC champ and TV presenter
Jason Plato, serveral times... he smokes like a chimney!
... since we're on touring car drivers, met BTCC ace
Mat Jackson in a pub, since then always went and said hello at the races I attended... nice bloke. Ex BTCC and current Porsche Super Cup driver
Stephen Jelly... really really nice bloke.. also
Matt Neal,
James Thompson,
Colin Turkington,
Rob Collard....
Tom Onslow-cole (nice bloke) and
Tom Chilton a couple of times (nice bloke-ish) and
Ex STIG, Ben Collins! Ex A1GP GB driver
Robbie Kerr... had a chat to him whilst wondering around at BTCC event.
Touring Car LEGEND
Deiter Quester.. don't think he spoke English.. conversation was kinda one sided!...
WTCC driver
Rob Huff... he was alright, invited me into his pit garage

, then told me to put that **** in the bin, referring to my andy Priaulx cap.
Christiano DaMatta,
Christian Klien,
Christijan Albers,
Christian Horner (a couple of times)... Horner is a really nice bloke, joked with him on two occasions about offering Juan Montoya a drive back in F1!
.... whilst
Juan Montoya himself, rolled his eyes at me, and went off in a huff
Tonio Liuzzi, whilst we were talking a woman came up and asked him to sign a picture of David Coulthard!
Nick Heidfeld, nice bloke, I tried to joke about my beard not being as good as his, he didn't laugh.
Met
Dirk Werner briefly at Silverstone this year.
..
Non motorsport related people..
Patrick Stewart in New York back in 2000, Thunderbirds creator
Gerry Anderson was a friend of a family members friend (tenuous, but I did meet him)...
I also met a porn star once, I don't remember her name, honest
umm, I'm sure there's been more...